Plot hole: For a convicted murderer who violated her parole and assaulted her parole officer while escaping custody, Ashley Judd moves around the country and even boards airplanes with little to no problems.
Suggested correction: She was simply careful. There's constant manhunts for much more serious felons and parolees on the lam who seem capable of moving around without getting caught.
How did she keep the gun if she flew across the country?
She likely put the gun in her bag and then checked it with other passengers' luggage at the airport. As long as she wasn't carrying the gun on her, it would go through.
Plot hole: Given the flimsy evidence of her husband's 'murder', (for a victim uttering his final words, he would not have been able to so state the exact coordinates of the boat). Any competent lawyer would have got her off. Also, her son Maddy then lives with daddy and his new girlfriend, aware that mummy is in prison for murdering him having visited her there. Surely he would have mentioned this to someone like his teacher etc?
Suggested correction: After receiving the fake message, the police found her alone on the blood-covered boat with the murder weapon. That kind of evidence is hard to shake off. As for Matty, he may have visited her in prison but it's highly unlikely that he knows why she is there or even remembers at his age. Later, he reveals that his dad told him that she was dead. If she died in prison, that isn't something that he would likely want to tell teachers or classmates.